Effect of Temperature and Time on the Conversion of Defatted Microalgae Biomass into Bio-Oil through Hydrothermal Liquefaction

The growing demand for renewable energy has increased interest in bio-oil production from microalgae biomass using hydrothermal liquefaction (HTL). However, limited research has focused on the utilization of defatted microalgae biomass (DMB), the residual biomass remaining after lipid extraction. Therefore, this study investigated the effect of varying operating conditions on the conversion of DMB derived from Chlorella sp. into bio-oil via HTL. Experiments were conducted at reaction temperatures ranging from 210–270 °C and reaction times between 30 and 90 min. The resulting bio-oils contained a range of compounds, including aliphatic acids, amines, amides, pyrazine, pyridine, and phenolic compounds. The highest yields of desirable aliphatic acids were obtained at 250–260 °C and 45 min, indicating these as optimal conditions for maximizing fuel-relevant components. While higher temperatures and longer reaction times promoted the formation of nitrogenous and aromatic compounds, they also introduced instability in the product composition. Hence, this work highlights the importance of optimizing HTL parameters to enhance bio-oil recovery from DMB.